Stabilization of vinyl ether polymers



- Patented Feb.,26, 1946 2,395,684 STABILIZATION or VINYL ETHER POLYMERS Calvin E. Sohildknecht, Easton, Pa., assignor to General Aniline & Film Corporation; New York,

N. Y., a corporation of Delaware No Drawing. Application December 23, 1944, Serial No. 569,654

12Clalms.

This invention relates to the stabilization of vinyl ether polymers and to the stabilized polymers.

The vinyl ether polymers are sensitive to heat and by this agency suffer depolymerization or breakdown in molecular weight, chiefly to lower polymers and the alcohols from which the vinyl carbon disulflde, benzene, etc., adding the sta bilizer to the solution, either in the solid form or as a solution or suspension in a further quantity ether monomers were derived. secondarily, the alcohols mayundergo air oxidation to aldehydes,

ketones. or acids. -Impending upon the temperature and length ofth'e exposure. the polymers lose their valuable properties to varying degrees, for example, the higher molecular weight polyof the solvent, using it necessary a small amount of another volatile organic liquid to promote solubility of the stabilizer in the solvent, and stir ring to efiect a fine dispersion of the stabilizer in the polymer solution, For example, where a solid rubbery polymer is treated in the foregoing manner and it is desired to regain the rubbery form'of the polymer in the stabilized condition,

more are subject to loss in their rubber-like properties of pressure tack, elasticity, nerve, and formstability. -While the-depolymerization is-more' rapid at elevated temperatures, it is not limited thereto, but takes place even at room temperature in contrast to the-behavior of polystyrene" and methyl methacrylate polymers which sufler depolymerization only at relatively elevated temperatures. e. g., at 200-300 C.

This sensitivity of the polymers to heat is a serious hindrance to their successful application in the arts, particularly in respect to the use of the medium to high molecular weight rubberlike polymers as substitutes for rubber, for example, in the preparation of pressure adhesives. It is, accordingly. desirable to protect them against thermal depolymerization and resulting loss in valuable properties.

- I have found that depolymerization of the vinyl ether polymers by heat may be retarded by inthe solvent is evaporated from the solution in a warm atmosphere, e. g., at about 50 C., at nor-' mal pressure or under a vacuum, to recover the. rubbery polymer in the stabilized condition; The. stabilizer also may be incorporated in the rubbery polymers by mixing in a Wern'er-Pfieiderer mixer.

As it is advantageous to add the stabilizer to the freshly formed polymers before objectionable depolymerization has taken place, the stabilizer may be added to the polymer in the polymerization vessel during the quenching or inactivation of the catalyst in the acid-catalyst type polymerization process. -In this process the polymer is stirred in the reaction vessel with sufficient of an agent in the form of an aqueous alkaline compound, e. g., concentrated ammonium hydroxide, to neutralize or inactivate the acid catalyst, preferably accompanied by a quantity of methanol.

The stabilizer is added along with the quenching agent and stirred intothe polymer at the same corporating in the polymers as a stabilizer therefor, a fine dispersion of. a small amount of the sulfide or polysufide of an alkali metal or alka-- line earth metal. g

The amount of the sulfide or polysulfide, e. g.,

time;

Stabilization according to the invention may be applied to the polymers of any of the vinyl others, for example, tothose described in United States Patent No. 2,104,000, e. g., to the polymers of sodium sulfide, potassium sulfide, calcium sulfide,

magnesium sulfide, sodium polysulfide, calcium polysulfide, etc., added to the polymers will depend on the degree of stabilization desired there- .in. Sodium sulfide and sodium polysulfide con:

stitute preferred stabilizers from the standpoint of cost and activity. In general, from about vinyl isopropyl ether, vinyl n-butyl ether, vinyl isobutyl ether, etc., to protect them against the effect of heat, while at the same time aflording them also a measure of protection against the depolymerizing eflect of light and air. The polymers may be, for-example, in the form of prod- 0.05-3% of the stabilizer on the-weight of-the' polymerwill be effective in retarding depolymerization and conserving the inherent physicalcharacteristics of the polymers on'exposure to heat.

The stabilizer should be finely divided, e. g., of about 1-10 microns in particle size, and finely 7 dispersed in the polymer for best results. Fine dispersion of the stabilizer in the polymers may be accomplished by dissolving the polymer in a 1 suitable volatile organic solvent, for example, in the low reaction temperatures, for example, a-

note which are viscous liquids, balsams, waxes. or soft resins as described in the aforesaid patent,

or in the form of rubber-like products of higher: molecular weight, e. g., the rubbery vinyl isobutyl 1 ether polymers described in United States Patent No. 2,061,934. vinyl ether, rubbery polymersmay be obtained,

for example, by the polymerization of the vinyl ether monomer at low temperatures, e. g., from about -40 C. to above about 0., in the presence of a. liquid organic diluent for the mon- Depending upon the particular omer which is a now-solvent for the polymer at liquid or liquefied hydrocarbon or a chlorinated hydrocarbon, e. g., propane. butane, methylene chloride, etc., and a suitable acid-reacting cat- 7 alyst of the kind described in the aforementioned patents, .e. g., boron fluoride or boron fluoridediethyl ether addition compound, the catalyst be-' ing quenched after the polymerization, the polymer recovered from the diluent as by filtration,

- under a vacuum.

The vinyl ethers employed in the production of the polymers may be those obtained from the reaction of acetylene and the corresponding alcohols, which monomers have been subjected to washing with water to remove alcohol and any aldehyde present. In some cases it may be necand dried at about 50 C. at normal pressure or essary to further purify the monomers as alco hols and aldehydes are inimical to the functioning of acid-reacting catalysts. This further purification may be accomplished by allowing the monomers to stand over powdered potassium hydroxide or metallic sodium for about 24 hours and then fractionally distilling them from the solid treating agent. One precise fractional distillatlon is generally sufilcient.

- The efiect of the alkali metal and alkaline earth metal sulfides and polysulfides in stabilizing the polymer still retained substantially'all of its rubpolymers against depolymerization by heat may be demonstrated in'the terms of the viscosities of the stabilized and unstabilized polymers before and after heating. The drop in viscosity of the polymers after exposure to heat is a measure of the degree to which depolymerization has taken place therein, the greater this drop, the corre-.

spondingly greater thedepolymerization and consequen'tloss oi" physical properties therefrom. All viscosities mentioned herein are specific viscosithree hours and then made up in benzene solution in the proportion of 1 gram or polymer per 100 ml. of benzene. The viscosities of the poly-' mers were determined by means of the benzene solutions in an Ostwald-Fenske capillary viscometer at 25 C. The polymer containing the dispersed sodium sulfide showed a specific viscosity of 4.9 as against a value of 0.70 for the control Polymer. As is apparent from a comparison of the respective viscosity values, the unstabilized polymer sufiered extensive depolymerization becoming a soft, sticky mass, whereas the stabilized bet-like character. g

I Example 2 Samples of the vinyl n-butyl other high 901!- mer oi specific viscosity described in Example 1 were made up in benzene-methanol solution, a stabilizer in the form of 1% of finely ground sodium polysulfide on the polymer added to one or the solutions, and the solutions or the test and control polymers subjected to evaporation of the solvent to recover the rubbery polymer, all

in the manner described in Example 1. The dried polymers were then heated in air at 150 C. for three hours.

Determination of the specific viscosities oi the heat-exposed polymer samples at C..showcd the following results: specific viscosity 0! the sodium polysulfide containing polymer=l.7; specific viscosity of the control polymer=0.7. It is readily apparent from these comparative viscosities calculated from relative viscosities determined in an Ostwald-Fenske capillary'viscometer at 25 C. on benzene solutions of the polymer samples made up in the proportion of 1 gram of the polymer in 100 ml. of benzene. I

The invention is further illustrated by the following specific examples to which, however, it is 3 not to be limited. Parts'areby weight and via-- cosities were determined as'described above;

' Example 1 ties that the unstabilized polymer sufiered a con.

siderably greater degree of depolymerization on exposure to'the heat.

' Emmple3 Into a further quantity of the rubbery viny 4 n-butyl ether polymer described in the previous Samples of a rubber-like high polymer of vinyl I ratio of 10 parts of the polymer to 100 parts of the solvent.

To one oi. the solvent solutions of the polymer was added 2% of finely ground sodium sulfide on the weight oi the polymer and the whole well stirred to disperse the stabilizer therein. To the other solution no addition was made. The solvent was then evaporated from the solutions at 50" C. under vacuum torecover the polymers in rubbet-like condition. I

The dried rubber-like polymers. the one containing sodium sulfide dispersed therein and ,the other not containing the stabilizer and constitutlnii the control, were heated in air at 100 C. for

thealkalimetal sulfideissodium sulfide.

4. A process of improving the resistance'iode l ym rization by heat of a' polymerized vinyl isop wl ether which comprises finely dispersing examples was incorporated 1% of finely divided calcium polysulfide on the polymer following the procedure oi these examples. A'control without the stabilizer waslikewise prepared. The polymer samples were then heated in air at C. for one hour. Determining viscositles oi the heat exposed polymer samples as before showed a specific viscosity tor the calcium polysulfide containing polymer of 1.1 and for the control polymer a value of 0.8. Here again it is apparent from the viscosity values that the unprotected polymersufiered greater depolymerization; Iclaim: l. A process of improving the resistance to de polymerization by heat of a polymerized-vinyl ether which comprises finely dispersing therein from about .05-3% of amember oi the groupconsisting of the alkali metal and alkaline metal sulfides and polysulfides. a 2. A process of improving the resistance todepolymerization by heat of a polymerized vinyl ether'which comprises finely dispersing therein from about .05 -'3% of an alkali metal sulfide.-

8. The process as definedin claim 2,-wherein therein from about Alli-3% of sodium sulfide.

5. A process of improving the resistance to dc.- polymerization by heat of a polymerized "vinyl n-butyl ether which comprises finelyidispcrsing therein from about,.05-3% of sodium sulfide;

6. A process of'improving the resistanceitmde polymerization byheat or a polymerizedlvinyl ascaoss to depolymerization by heat in which is finely dispersed about .05-3% of an alkali metal sulfide.

9. A vinyl ether polymer or improved resistance to depolymerization by heat in which is-finely dispersed about 954% or sodium sulfide.

10. A vinyl isopropy ether polymer of improved resistance to depolymerizatlon by heat in which is finely dispersed about .053% of sodium sulfide.

11. A vinyl n butyl ether polymer of improved resistance to depolymerization by heat in which is finely dispersed about 354% of soduim sulfide.

12. A vinyl isobutyl ether polymer of improved I resistance to depolymerization by heat in which is finely dispersed about Alli-3% or sodium sulfide.

CALVIN E. a: 

